March 22 notes: eggs over easy ...

You may have noticed that the eagles occasionally take a brief respite from incubation and seem to be arrange items in the middle of the nest. Eagles, like all birds, need to turn their eggs frequently during incubation. An air cell forms in the egg shortly after the egg is layed and grows larger during incubation. The parents need to turn the egg to prevent the developing embryo from adhering to the eggs shell, which stops development. As far as we know, biologists have not documented how often eagles turn their eggs. Perhaps you can gather some information on this behavior by watching the web camera.

Bald eagles typically lay only one clutch per year. Eagles on the coast of Maine may lay a clutch as early as mid-February, although early March is more typical. In northern Maine, where the lakes are still frozen over and the snow pack still has weeks before it melts, egg-laying may be delayed into early to mid-April. We have seen eagles many times blanketed in an early spring snow, but remaining faithful to their incubation duties.

Bald eagles lay one to three eggs, but two is most common. They are dull white in color and about the size of a goose egg. The eggs are layed about 3 or 4 days apart. Incubation begin when the first egg is layed, which means that eggs in a clutch will hatch several days apart. "Asynchronous hatching" is a common in strategy in birds of prey. One chick will always be the oldest and largest and dominant over its siblings. In poor food years, only the oldest chick may survive, but in good years all chicks in a brood survive.

Both the male and female eagle develop a brood patch - a bare area of skin in the center of the chest to keep the eggs warm. the female eagle does most of the incubating, but the male also returns to the nest to help. If you're lucky, you may see a nest exchange occur on the web camera. The male will often bring food to the nest for the female while she is incubating.

Adults show great concern for their fragile eggs and walk very carefully around the nest with clenched feet to avoid breaking the eggs. We would be interested in hearing from you if you observe no eagles on the nest during the incubation period. Adults will occasionally leave the eggs for a brief time (perhaps on warmer days in late incubation). If they do, they sometimes cover the eggs with grass and pine needles from the nest bowl to avoid predation by crows. -- Mark McCollough, U. S. Fish and Wildlife Service